Recently, development of compact and high-performance electronic devices, including notebook computers as a typical example, is remarkable. Accordingly, there is a strong demand for miniaturization and space-saving of a cooling structure equipped to cool a heating component such as an MPU mounted on such electronic devices. Under these circumstances, it is also demanded to develop a high-performance and thin heat pipe to be included in a cooling structure of this type.
A heat pipe is a component produced by sealing condensable fluid functioning as working liquid into a container such as a closed vacuum-deaerated metal pipe. The heat pipe automatically operates by utilizing temperature differences. The working liquid evaporated in a high-temperature area flows toward a low-temperature area, and releases heat and condenses thereat, so as to transport heat as latent heat of the working liquid.
More specifically, a space functioning as a channel for the working liquid is formed inside the heat pipe. The working liquid contained in that space undergoes phase changes such as evaporation and condensation, and shifts through the space to transfer heat. The working liquid is evaporated on the heat receiving side of the heat pipe by heat of a cooling-target component conducted by heat conduction through the material of the container constituting the heat pipe. The vapor thus produced shifts toward the heat releasing side of the heat pipe. On the heat releasing side, the vapor of the working liquid is cooled and returns to the liquid-phase condition again. The working liquid returned to the liquid-phase condition again shifts (circulates) toward the heat receiving side. Heat transport is achieved by utilizing the phase changes and shift of the working liquid caused by this mechanism.
When the working liquid condensed in the foregoing heat releasing area does not return to the heat receiving area, the operation of the heat pipe does not continue. Accordingly, it is needed that the working liquid condensed in the heat releasing area is rapidly circulated to the heat receiving area. For meeting this necessity, such a method is known which disposes a wick (sheet-shaped wick or wire, for example) capable of producing capillary effect within the container of the heat pipe. Another known method forms fine grooves in the inner wall of the container. Moreover, such a heat pipe is known which contains a laminated mesh member so as to improve the heat transport performance (for example, refer to Patent Literature 1 and Patent Literature 2).